Date: Sun, 20 Mar 2005 13:25:02 +0100 (MET)
From: Jan Engelhardt <jengelh@linux01.gwdg.de>
To: linux-kernel@vger.kernel.org
Subject: Short sleep precision
Message-ID: <Pine.LNX.4.61.0503201316320.18044@yvahk01.tjqt.qr>
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Sender: linux-kernel-owner@vger.kernel.org
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Hello,


I have found that FreeBSD has a very good precision of small sleeps --
what's holding Linux back from doing the same? Using the code snippet below, 
FBSD yields between 2 and 80 us on the average while Linux is at 
"constantly" ~100 (with HZ=1000) and ~1000 (HZ=100).


Jan Engelhardt
-- 

#include <sys/time.h>
#include <stdio.h>
#include <time.h>
#define MICROSECOND 1000000
static unsigned long calc_ovcorr(unsigned long ad, int rd) {
    struct timespec s = {.tv_sec = 0, .tv_nsec = ad};
    struct timeval start, stop;
    unsigned long av = 0;
    int count = rd;

    while(count--) {
        gettimeofday(&start, NULL);
        nanosleep(&s, NULL);
        gettimeofday(&stop, NULL);
        av += MICROSECOND * (stop.tv_sec - start.tv_sec) +
         stop.tv_usec - start.tv_usec;
    }

    av /= rd;
    fprintf(stderr, " %lu us\n", av);
    return av;
}

int main(void) {
    calc_ovcorr(0, 100);
    return 0;
}

//eof
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